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 Post subject: Fuel Pumps
PostPosted: Sun Feb 24, 2019 10:57 pm 
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Joined: Sat Sep 28, 2013 6:41 pm
Posts: 8
Location: London or Ibiza
model: 750 Paso
year: 1987
I am just about to get the bike back on the road again after a long storage and as a part of the restoration I have been using knowlage gained from here.

I changed to the Mikuni fuel pump and I wish I had known about it 5 years ago however anyone buying second hand as I did should be aware that what they buy will almost certainly need a service kit.
It's a very simple job to do and will set you back around £11 if you are in USA or £22 in Europe

If you don't service it it may work but probably won't be reliable in that it will pump from start up but stop after about 10mins

Andy


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 Post subject: Re: Fuel Pumps
PostPosted: Tue Feb 26, 2019 7:08 am 
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paso grand pooh-bah
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Joined: Wed Dec 05, 2007 12:35 am
Posts: 1686
Location: Newzealand
model: 906 Paso
year: 1990
Andy ,having just replied to your icing thread and now I see this one ....without knowing the timing of these events ,did these issues overlap ? if so I could think they were connected and would wonder if you didn't have maybe a (partially) blocked tank vent. Can't help but think that a mikuni diaphram pump that worked for the 1st 10 mins would go all day and the time it takes for a carb to warm up could actually be the time it takes for a tank with a blocked vent to equilise and allow fuel to flow adequately again . Just thinking that's all :)

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 Post subject: Re: Fuel Pumps
PostPosted: Wed Feb 27, 2019 11:03 am 
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Joined: Sat Sep 28, 2013 6:41 pm
Posts: 8
Location: London or Ibiza
model: 750 Paso
year: 1987
Hi :)

The fuel tank and pump are parts I picked up to get the bike back on the road after a long period gathering dust.
The reason she came off the road was that the original fuel tank started leaking from the bottom seams :(
The electric pump works fine and I had also fitted an adjustable regulator but the vacuum pump is a much neater solution.
When I had put it all back together and was testing it in the garage my initial thought was fuel starvation due to the tank not venting but that was clear.
I stripped the pump and found that the flexible membrane that makes the pump work was dome shaped (should be flat) and in effect it was staying in the roof of the vacuum chamber instead of returning to flat and pushing the fuel out.
I'm not sure why it would work for a short while and then stop... Possibly after 30min standing the membrane shrank back a little?

Whatever the reason the rebuild kit was reasonable and the design has changed slightly as now they have 2 x membranes (one each side).

All the best, Andy


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 Post subject: Re: Fuel Pumps
PostPosted: Wed Feb 27, 2019 3:40 pm 
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paso grand pooh-bah

Joined: Thu Jun 21, 2007 12:00 am
Posts: 1473
Location: Gothenburg, SWEDEN
model: 907 I.E.
year: 1991
I also had a 45 minute fuel pump on my Monster. Then I had to limp home w almost no throttle.
Same next day etc. New diaphragm solved it, these pumps can have a semifailed function.

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907 I.E. -91
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